Most late-term abortions would be outlawed in the United States under legislation which Republicans pushed through the House of Representatives.

The plans are a major priority of the GOP and conservative groups but do not look likely to reach the desk of president Donald Trump because they face certain defeat in the Senate.

The House approved the measure by a near party-line 237-189 vote.

Though the bill's fate is sealed, the push for abortion restrictions remains a touchstone issue for most Republicans, even as the party splinters between traditionalist conservatives and anti-establishment voters looking to rile Washington.

Mr Trump was ready to sign the measure, and White House officials sent politicians a letter saying the measure "would help to facilitate the culture of life to which our nation aspires".

That praise was in contrast to the certain veto similar bills faced under president Barack Obama.

The Democratic-controlled Senate didn't even consider one bill the House approved in 2013, and a House-passed measure in 2015 fell short in a GOP-run Senate.

That same fate awaits it this year. Republicans have a 52-48 Senate majority but overwhelming Democratic opposition means the measure would never reach the 60 votes it would need to pass.

The White House letter also said "recent advancements" show "the physical structures necessary to experience pain" are developed 20 weeks after fertilisation.

During Tuesday's debate, Republicans said there is scientific evidence backing that view, including ultrasound images of fetuses reacting to being prodded.

"These unborn babies are feeling pain. They suffer. That is really hard to hear and really hard to say," said House Speaker Paul Ryan.

Democrats rejected that, calling such assertions junk science.

The American Congress of Obstetricians and Gynaecologists has said fetuses cannot experience pain before at least 24 weeks of development.

In an interview, the group's chief executive officer, Hal Lawrence, said "the overwhelming amount of evidence" shows fetuses younger than that have reflex activity but lack the neurological development to sense pain.

Representative Louise Slaughter, called the measure the GOP's latest attempt "to pass off political posturing as proven science".

Reverberations from Sunday's mass shooting in Las Vegas spilled into the debate, with some Democrats saying that barring automatic weapons was a better way to save lives.

But most avoided merging the two issues and focused instead on women's rights to choose abortion, a legal procedure.

"I'm a survivor of rape. That is painful," said Democrat Gwen Moore, adding: "This bill is a cruel and ruthless attempt to undermine women and attack our right to govern our bodies."

The measure would make it a crime for anyone to perform most abortions on fetuses believed to be 20 weeks into development. Violators could face five years in prison.

Exceptions would be made to save the mother's life and for incest and rapes reported to government authorities.

Abortions after 20 weeks are rare. According to the federal Centres for Disease Control and Prevention, of over 664,000 reported abortions in 2013, just 1.3 percent occurred at least 21 weeks into development.

The Supreme Court legalised abortion in 1973 but opened the door to some state restrictions. Forty-three states bar some abortions at certain points during pregnancies, according to the Guttmacher Institute, a research group that favours abortion rights.